Process for the preparation of fatty acid alkyl esters having improved processing properties

ABSTRACT

Lower alkyl esters of higher fatty acids with improved processing properties, particularly sulfonation, are obtained by subjecting lower alkyl esters of higher fatty acids of plant and/or animal origin, or said fatty acids per se, in the presence of esterification catalysts and/or carboxylic acid anhydrides, to a brief temperature treatment above 150° C., and separating simultaneously and/or subsequently, preferably by distillation, the purified lower alkyl esters of higher fatty acids or the purified higher fatty acids from the treated material and the purified higher fatty acids are then esterified with lower alkanols.

This application is a division of application Ser. No. 397,095, filedJuly 12, 1982, now U.S. Pat. No. 4,552,702.

BACKGROUND OF THE INVENTION

This invention relates to a process for the preparation of lower alkylesters of higher fatty acids having improved properties for processinginto surface-active α-sulfo-fatty acid esters.

The preparation of surface-active α-sulfo-fatty acid esters from fatsand oils especially of natural origin, has been known for years. Forexample, U.S. Pat. No. 2,195,187 describes α-sulfo-fatty acids and theiresters as surface-active compounds or surfactants. They are obtained bythe sulfonation of lower alkyl esters of saturated higher fatty acidswith sulfur trioxide. The lower alkyl esters of higher fatty acids areobtained by reesterification of hydrogenated fats or oils withmonovalent, lower alkanols, especially methanol, or by the cleavage ofglycerides and subsequent esterification of the fatty acids.

Henkel KGaA has been concerned intensively with this class ofsurface-active α-sulfonated fatty acids and respective fatty acid estersas well as their salts. The German Published Application DE-AS No. 12 46718, for example, describes a process for the preparation of this classof compounds. Fatty acids and fatty acid esters that have 6 to 28 carbonatoms in the fatty acid radical, have no other groups that can besulfonated or sulfated beside the carbon atom in α-position, and have aniodine number of less than 5, are sulfonated with a mixture of sulfurtrioxide and inert gas, and the reaction product is neutralized. Aparallel procedure working with the same substances is described inDE-AS No. 12 48 645.

One of the main problems of the area involved here is the colorinstability of the lower alkyl esters of higher fatty acids in thesulfonation step. The crude products obtained are dark colored,brown-black and must be processed into light-colored products for use inwashing and cleaning agent compositions. While the color of the crudesulfonation products does depend to some degree on the workingconditions, the technical utilization of these, of themselvesinteresting possible starting materials, still is hampered by thefollowing principle: The higher the yield of the reaction in thesulfonation step (the degree of sulfonation), the darker the color ofthe reaction product and the greater the problems to obtainlight-colored end products.

The significance of the constitution of the fatty acids or the fattyacid mixtures to be sulfonated is considered as certain knowledge by theexperts in the field. Especially the stipulation is made that the fattyacids to be sulfonated in the α-position shall not have any doublebonds, or as few as possible, nor any other types of reactive groups,especially hydroxyl groups. With the selection of suitable fats or oils,this problem is limited to the removal of unsaturated bonds in the fattyacid molecule. These sources of interference are eliminated byhydrogenating the starting material as completely as possible before thesulfonation. The literature of the state of the art indicates requirediodine numbers of less than 5, preferably less than 2. Much lower iodinenumbers, that is, those in the range from 0.1 to 0.3, are used in thepractical examples.

The removal of interfering accompanying substances by distillation orother methods from the fatty acids or fatty acid mixtures to besulfonated is called for to reduce the discoloration problem, forexample in DE-AS No. 12 48 645.

However, bleaching of the crude sulfonic acid derivatives always isnecessary as final step in the process. The state of the art has evolvedparticularly two types of procedures for this purpose: Acid bleachingwith hydrogen peroxide, as described in German Patent DE-PS No. 11 79931, or combination bleaching in which the initial hydrogen peroxidebleaching is followed by the neutralization of the sulfonated andpartially bleached material, after which a final bleaching step isconducted, again with hydrogen peroxide or, more advantageously, withhypochlorite, as described in DE-AS No. 12 34 709, for example.

The problem of discoloration becomes particularly difficult when thesulfonation is to be increased to yields exceeding 90%, or even todegrees of sulfonation above 95%. The teachings of the DE-OS No. 14 43995 concern themselves with the problems arising from this. According toinformation in this published patent specification, sulfur trioxide hasa strongly decomposing effect on saturated fatty acid esters free ofalcoholic hydroxyl groups, and this results unavoidably in very dark,discolored sulfonation products in the preparation of highly sulfonatedproducts with a degree of sulfonation of at least 90%, preferably 94%,and especially at least 96%.

DE-OS No. 14 43 995 recommends the addition of water to the sulfonationor the sulfonation product in order to keep the discoloration withinlimits. But this method generates new problems for the practicalapplication in addition to observing certain temperatures. The viscosityof the sulfonated starting product in the strongly acid range isseriously affected by smallest amounts of water. Even the addition of 2%hydrogen peroxide in the form of a 35% solution causes a steep rise inviscosity with sulfonation products having a chain length of C₁₆ /C.sub.18. The danger of clogged lines can happen in the continuoustechnical-scale process.

According to the available experience, the various difficultiesdeveloping in different steps of the entire process force a compromisebetween the degree of sulfonation and bleaching. The optimal degree ofsulfonation obtainable in practice are close to approximately 90%.

It is common knowledge that natural starting materials such as plantand/or animal fats or oils generally are subject to certain variationsin quality, due, for example, to the peculiarities of their originand/or their handling up to the planned further processing. Thesevariations bring with them a certain increase in problems in furtherprocessing, in contrast to standardized, purely synthetic startingmaterials. Consequently, there exists in the respectively morecircumscribed field of the lower alkyl esters of higher fatty acids, aneed for the standardization of the product quality of differentstarting materials by a simple refining procedure as well as forimprovement of the processing characteristics of the refined materials,which guarantees dependable and improved subsequent processing resultsand/or products with improved characteristics in the large-scaleoperation.

OBJECTS OF THE INVENTION

An object of the present invention is the development of a process forthe preparation of lower alkyl esters of higher fatty acids withimproved processing properties by a simple refining procedure.

Another object of the present invention is the development of a processfor the preparation of lower alkyl esters of higher fatty acids withimproved processing properties comprising the steps selected from thegroup consisting of

(A) subjecting lower alkyl esters of higher fatty acids of plant and/oranimal origin, to a heat treatment above 150° C., in the presence of aneffective amount to reduce the hydroxyl number of a material selectedfrom the group consisting of esterification catalysts and carboxylicacid anhydrides, for a time sufficient to effect an improvement infurther processing properties, separating purified lower alkyl esters ofhigher fatty acids from the treated material and recovering said loweralkyl esters of higher fatty acids with improved processing properties,and

(B) subjecting free higher fatty acids of plant and/or animal origin toa heat treatment in the presence of an effective amount of reduce thehydroxyl number of a material selected from the group consisting ofesterification catalysts and carboxylic acid anhydrides, for a timesufficient to effect an improvement in further processing properties,separating purified higher fatty acids from the treated material,esterifying the purified higher fatty acids with a lower alkanol underesterification conditions, and recovering said lower alkyl esters ofhigher fatty acids with improved processing properties.

These and other objects of the present invention will become moreapparent as the description thereof proceeds.

The invention is based on the objectives of the requirement of obtaininga uniform starting material for further processing, particularly bysulfonation, which product has improved processing properties. With it,the described problems of discoloration of alkyl esters of fatty acidsor their mixtures during sulfonation are to be reduced, for example. Theinvention is an attempt to create, in a limited sense, a pretreatmentfor the alkyl esters of fatty acids to be sulfonated, which makes aneffective curtailment of the discoloration in the subsequent sulfonationstep possible. On the other hand, the invention is an attempt at thestandardization of the fatty acids or alkyl esters of fatty acids fromnatural sources, by a simple refining procedure, to permit reproducibleprocessing results, for example, during the sulfonation of the alkylesters of fatty acids. In particular, the invention is also an attemptto adapt starting materials of lower quality to the subsequentpurification steps into high-quality materials.

The technical solution of the objects of the invention is based on thediscovery that the desired goal is achieved if the alkyl esters of fattyacids are subjected to a thermal pretreatment under specific conditionsgiven below, of if the free fatty acids are subjected to thispretreatment and are subsequently esterified with the correspondingalcohols.

Thus, the subject of the invention is a process for the preparation oflower alkyl esters of higher fatty acids with improved processingproperties from higher fatty acids of plant and/or animal origin. Theprocess according to the invention is characterized by the fact

(A) that the starting material containing the lower alkyl esters ofhigher fatty acids is subjected to a relatively brief temperaturetreatment above 150° C. in the presence of esterification catalystsand/or carboxylic acid anhydrides, and the so-reacted lower alkyl estersof higher fatty acids are separated from the added adjuvants and smallamounts of high-boiling substances formed during the treatment,preferably by distillation, or

(B) that the starting material containing free higher fatty acids issubjected to a relatively brief temperature treatment in the presence ofesterification catalysts and/or carboxylic acid anhydrides, theso-treated higher fatty acids are separated from the added adjuvants andsmall amounts of high boiling substances formed during the treatment,preferably by distillation, and the purified free higher fatty acids areesterified by lower alkanols in a conventional manner.

More particularly, the present invention relates to a process for thepreparation of lower alkyl esters of higher fatty acids with improvedprocessing properties comprising the steps selected from the groupconsisting of

(A) subjecting lower alkyl esters of higher fatty acids of plant and/oranimal origin, to a heat tratment above 150° C., in the presence of aneffective amount to reduce the hydroxyl number of a material selectedfrom the group consisting of esterification catalysts and carboxylicacid anhydrides, for a time sufficient to effect an improvement infurther processing properties, separating purified lower alkyl esters ofhigher fatty acids from the treated material and recovering said loweralkyl esters of higher fatty acids with improved processing properties,and

(B) subjecting free higher fatty acids of plant and/or animal origin toa heat treatment above 150° C. in the presence of an effective amount toreduce the hydroxyl number of a material selected from the groupconsisting of esterification catalysts and carboxylic acid anhydrides,for a time sufficient to effect an improvement in further processingproperties, separating purified higher fatty acids from the treatedmaterial, esterifying the purified higher fatty acids with a loweralkanol under esterification conditions, and recovering said lower alkylesters of higher fatty acids with improved processing properties.

This temperature pretreatment is performed preferably in the range up toapproximately 280° C. and especially in the temperature range from about200° to 250° C. Temperatures in the range from 200° to about 230° C. canbe especially advantageous. The treatment conditions and especially thetreatment temperature and the time the starting material to be purifiedremains at this temperature under the process conditions are mutuallyadjusted, preferably in the manner to be described in the following.

The duration of the pretreatment according to the invention, that is,the time the alkyl esters of the fatty acid or the free fatty acidstarting material remains under the treatment conditions, is generallyrelatively brief. It may last for up to 15 minutes, for example, butconsiderably shorter times can be used in preferred practical examplesof the invention. If needed, the thermal pretreatment according to theinvention can be extended, for example, up to 30 minutes or also toabout one hour. However, no significant processing advantages aregenerally connected with this extension.

In the preferred practical example of the invention, the conditions ofthe refining step according to the invention, and here especially thetreatment temperature and the time the material is treated, are mutuallyadjusted so that an esterification or reesterification of free hydroxylgroups can take place, preferably without any other substantialalteration in the structure of the alkyl esters of the fatty acid or thefree fatty acid. This measure according to the invention becomescomprehensible with the following explanation. The alkyl ester of thefatty acid or the free fatty acid starting material apparently containsinterfering components, which are present in varying quantitiesdepending on orgin and individual history of the respective alkyl esterof the fatty acid or free fatty acid material. These interferingcomponents obviously are compounds that are hydroxylated on the chain,which may be present only in trace quantities but make themselves knownby a disproportionate interference during the subsequent processing,possibly after esterification, of the alkyl esters of the fatty acids.With the temperature pretreatment under the given conditions, theprocess according to the invention is designed to create the possibilityof obtaining a standardized, purified alkyl ester of a fatty acidproduct that does no longer have the described advantages in thesubsequent processing phases. The pretreatment according to theinvention actually allows the separation of smallest quantities ofinterfering accompanying substances from the fatty acid esters or freefatty acids that are not hydroxylated on the chain by a simple reaction.The esterification or reesterification of the components containing freehydroxyl groups with the ester or carboxyl groupings of the reactionmaterials present in an excess and/or the reaction with the addedcarboxylic acid anhydrides brings about such a shift in the boilingpoint of these interfering admixtures that the separation of thepurified main part of the fatty acid esters or free fatty acid startingmaterials used from the formed high-boiling substances by distillationbecomes possible. Alkyl esters of fatty acids or free fatty acids ofnatural origin usually are mixtures of varying amounts of saturated andunsaturated compounds, as they were obtained from the respective fats oroils of natural origin. Because of their individual histories ofpreparation and storing, mixing or blending and additional influences ofthis type, starting materials with widely varying qualifications must beexpected in practice. The conversion of any different startingmaterials, by one constant method, into a product that can be processedmore readily in one of the described following processing phases and/orwill lead to improved end products, is possible with the pretreatmentaccording to the invention.

The reactive purification according to the invention can be facilitatedby working under reduced pressure. Such a reduction in pressure shouldaccelerate the shift in the equilibrium during the reesterificationreaction between hydroxyl groups on the chains and the terminallylocated ester or carboxyl groupings, with the cleavage and removal ofthe monofunctional alcohol if the alkyl ester of fatty acid is used. Ina preferred practical example, the work proceeds at such a reducedpressure that the distillation of the lower alkyl esters of fatty acidsor the free fatty acids freed of interfering components becomes possibleeither simultaneously with or immediately following, the refiningtreatment according to the invention. For example, working withpressures in the range from 0.05 to 10 torr, particularly in the rangefrom about 0.1 to 5 torr, can be especially advantageous. The combiningof the temperature pretreatment according to the invention for thereactive elimination of the interfering components and the separation bydistillation of the purified material into a preferably continuouslyoperating phase of the process is possible in this manner. The reactiveconversion of the interfering accompanying components into high-boilingsubstances is accomplished in surprisingly short time spans that may bein the range of seconds or even fractions of a second. For example, itis possible according to the invention to add esterification catalystsand/or carboxylic acid anhydrides to the starting material to bepurified and to distill the mixture, while maintaining the pottemperature of the material to be distilled above 150° C. and preferablywithin the temperature range particularly suitable according to theinvention. Thermal pretreatment and separation of the undesirable partsof the product thus are practically combined into one step of theprocess. Another especially technically simple modification providesthat the esterification catalysts and/or carboxylic acid anhydrides,dissolved, for example, in a high-boiling substance, are charged in thetemperature range of the pretreatment according to the invention andunder reduced pressure. The starting material to be purified is fed intothis reaction zone either proportionately or preferably continuously.Pressure and temperature conditions are mutually adjusted to guaranteethe distillation of the major part of the fatty acid ester or free fattyacid material. Despite the very fast vaporization of the startingmaterial fed into the reaction zone, the interfering components areconverted by reaction at such a rate that the collected distillate hasthe desired improved processing properties.

Especially in these latter practical examples of the simultaneousreactive purification and distillation, the work may proceed withholding times at the desired temperature in the range from about 0.1 to3 minutes, for example, with temperatures preferably in the range fromabout 200° to 250° C.

Esterification catalysts and/or carboxylic acid anhydrides are used asactive additives in the process according to the invention. Anyesterification catalysts from the extensive present state of the art maybe used for this purpose. However, the work is performed preferably withbasic, neutral or at most weakly acid catalysts or catalytic systems.Especially preferred is to conduct the work with catalysts that aresoluble in the starting material to be purified and/or in high-boilingsubstances, which are formed during the process according to theinvention and/or are used in purification according to the invention inthe sense described above. The use of liquid, soluble catalysts orcatalytic systems can be particularly expedient.

The compilation in J. Am. Oil Chem. Soc. 55: 796-805, 1978, especiallythe compilation that Table I on page 797, is cited simply as an examplefrom the extensive state of the art concerning the esterificationcatalysts. Listed are metal salts such as acetates, carbonates,chlorides, nitrates and oxides of tin, zinc, iron, cobalt and lead;alkali metal hydroxides such as NaOH, KOH, LiOH; metal soaps such as thestearates of alkali metals, zinc, aluminum and titanium; alkali metalsor their alloys; metal alkylates and metal hydrides. Especially suitableare metal soaps of saturated and/or unsaturated monocarboxylic orpolycarboxylic acids with the carbon chain lengths C₂ -C₃₆ of thefollowing metals: K, Na, Li, Al, B, Zn, Sn, Ca, Mg, Ti and V; metallicalcoholates of saturated and unsaturated monohydric or polyhydric linearor branched alcohols with the carbon chain length C₁ -C₃₆ with thefollowing metals as cation: Li, Na, K, Mg, Ca, B, Al, Zn, Sn and Ti; themetal hydrides, that is, hydrogen compounds of the elements Li, Na, Mg,Ca, B, Al and Sn or their mixtures; and the metal alkyls, that is,carbon compounds of the elements Li, Na, Mg, Ca, B, Al, Sn and Ti, ortheir mixtures.

An especially suitable class of catalysts or active additives is derivedfrom soluble organic compounds of boric acid. Suitable are especiallyboric acid esters, for example, boric acid alkyl esters, among whichthose with relatively higher alcohols (C₁₀ -C₂₂, especially C₁₂ -C₁₈-alkanols) can be particularly preferred. But suitable are especiallyalso esters of boric acid with partial esters of polyhydric alcohols,for example, the respective esters of polyhydric alcohols with mono- ordiglycerides. These partial esters of polyhydric alcohols may also bederived from higher fatty aclohols, especially those in the carbon atomrange of from 10 to 22. Boric acid esters that are liquid and/or solubleat the process temperature are a preferred catalyst class. Additionalexamples of suitable boric acid compounds are boric acid anhydride,sodium borate and sodium boronate.

Carboxylic acid anhydrides can be used as active additives in additionto, or instead of, esterification catalysts in the temperature treatmentaccording to the invention. However, the concurrent use ofesterification catalysts that facilitate the reaction of the carboxylicacid anhydride with hydroxyl groups is preferred. The carboxylic acidanhydrides can be derived basically from monocarboxylic acids orpolycarboxylic acids, especially from dicarboxylic acids in this case.In one practical example of the invention, the use of relativelyhigh-boiling carboxylic acid anhydrides with a boiling point especiallyhigher than that of the fatty acid esters or free fatty acids to berefined, is to be preferred. For example, carboxylic acid anhydridesboiling above 300°C./1 torr can be suitable starting materials for theprocess of the invention. Such carboxylic acid anhydrides are derived,for example, from C₈ -C₂₈ -monocarboxylic acids, especially frommonocarboxylic acids with 10 to 22 carbon atoms (C₁₀₋₂₂ -fatty acids).Working with such high-boiling carboxylic acid anhydrides facilitatesthe process according to the invention inasmuch as possibly presentexcesses of this active additive can be readily removed from the refinedfatty acid ester or free fatty acid by a subsequent distillation.

Also included under the term carboxylic acid anhydrides according to theinvention are mixed acid anhydrides or carboxylic acids and inorganicacids, especially mixed acid anhydrides of higher fatty acids and boricacid. As explained, the fluidity of the reaction components used asadditives may be desirable for the performance of the process accordingto the invention in a continuous operation. Distillation residues fromthe known treatment of fatty acids, for example, those of naturalorigin, with boric acid compounds that contain a not inconsiderableproportion of fatty acid anhydrides, mixed boric acid/fatty acidanhydrides and/or boric acid, are a suitable additive for the refiningprocess according to the invention. These fluid distillation residuesthus can be used in an important, further process step.

The mentioned active additives (esterification catalysts and/orcarboxylic acid anhydrides) usually are added only in small quantitiesto the fatty acid ester or free fatty acid starting material to bepurified, although larger amounts are generally not harmful. Suitableare, for example, amounts from 0.01 to 20% by weight, especially amountsin the range from about 0.1 to to 10% by weight, of the active additiveor additive mixture, calculated with respect to the fatty acid ester orfree fatty acid starting material. Amounts of the active additive notexceeding 5% by weight, preferably not exceeding 3% by weight, willgenerally be used. The especially preferred range for the amount to beused lies between 0.05 and 1.0% by weight. All of these percentages byweight are based on the fatty acid ester or free fatty acid startingmaterial to be treated. When carboxylic acid anhydrides are usedtogether with esterification catalysts, the catalysts may be used in theusual small amounts, for example, their amount is from 0.001 to 10% byweight, especially from 0.01 to 5% by weight, calculated on thecarboxylic acid anhydride. When the above described continuous processis used, in which the starting material to be purified is added to areaction zone containing the esterification catalysts and/or carboxylicacid anhydrides, and purified fatty acid ester or free fatty acidmaterial is simultaneously removed from this reaction zone bydistillation, the only thing to be observed is the use ofreesterification catalyst and/or carboxylic acid anhydride in an amountthat is adequate to bring about the desired reactive removal of theinterfering components within the brief time span available for thereaction.

The purification of the lower alkyl esters of higher fatty acidsaccording to the invention does not necessarily result in an improvementin color nor in a substantial change in the parameters (hydroxyl number,iodine number, saponification number and/or acid number). The effect ofthe pretreatment according to the invention does not manifest itself inthe purified lower alkyl esters of higher fatty acids but only with itscontinued processing, that is, after the sulfonation of a startingmaterial pretreated by this method. In this case, it is expressed in thebetter bleaching qualities of the sulfonation product, for example.Bleached products with Klett color numbers of less than 60 can beprepared without any problems.

The pretreatment according to the invention can be carried out withfatty acid ester or free fatty acid fractions hardening by hydrogenationor still unhardened. When unhydrogenated material is treated, theobtained product fraction should be hardened as soon as possible toeliminate undesirable oxidative influences due to ageing via the doublebonds in the product.

A conventional separation of interfering components, presumably of theportions formed by oxidative ageing causing the hydroxylated methylester of fatty acids where the hydroxyl are located on the chain, fromthe problem-free parts of the starting material is practicallyimpossible. A distillation does not achieve the objective. The teachingsof the invention, that is, subjecting the starting material of anycomposition together with the active additives to the thermalpretreatment and especially distilling above this material, removes theexisting difficulties and yields reliably a starting material suitablefor the following sulfonation and bleaching.

The knowledge of the state of the art applies to the subsequentsulfonation and bleaching. Details for the performance of the acidbleaching or multiphase combination bleaching are found, for example, inthe German patents DE-PS Nos. 11 79 931 and 12 34 709 and the DE-OS No.14 43 995. The described sufonation is usually carried out attemperatures from 70° to 130° C. in a descending film reactor with amixture of gaseous sulfur trioxide and an inert gas, during a period of10 to 20 minutes and to give sulfonation degrees exceeding 90%especially exceeding 92% and, as a rule, exceeding 94%. Sulfonationdegrees of 95% and higher are especially preferred. Yet, sulfonationproducts with Klett number of 50 or less can be prepared reliably withthe use of the purification treatment according to the invention.

Suitable higher fatty acid ester starting materials are especially therespective lower alkyl esters with preferably 1 to 5 carbon atoms in thealkanol radical. Especially important are the methyl esters of higherfatty acids that were obtained from plant and/or animal fats byreesterifying or by saponification with subsequent esterification.

EXAMPLES

The following examples explain the pretreatment according to theinvention and its results along with comparison experiments that lieoutside the scope of the invention. These examples are not to be deemedlimitative in any respect.

The purification effect of the process according to the invention isjudged by the beachability of the ester sulfonate pastes obtained aftersulfonation.

The method of sulfonation and bleaching described below applies to allexamples:

Batches of 576 gm of a methyl ester of tallow fatty acids weresulfonated in a standing cylinder heated to 80° C. by blowing in, over aperiod of 65 minutes, a 5% by volume mixture of SO₃ in air, in such arate that the total amount contained 208 gm(2.6 mol) of SO₃, and asubsequent after-reaction period of 15 minutes. The crude sulfonic acidobtained was neutralized by the simultaneous addition of crude sulfonicacid and sodium hydroxide solution together to give a mixture in the pHrange from 6.5 go 8 to form an aqueous paste containing about 25%sulfonation product. This sulfonation product was bleached at 60° C.with 15.4% by weight, based on the sulfonation product, of a 13% aqueousNaOCl solution. A 5% aqueous solution of the sulfonation product,adjusted to pH 7, had a Klett number as mentioned in the individualexamples, when it was measured with the blue filter (420 mm) in a Klettround-glass cell on the Klett-photometer (Model 800-3 byKlett-Summerson). The degree of sulfonation of the pastes obtained wasbetween 95 and 97%.

COMPARISON EXAMPLE A

The starting material was a methyl ester of a hardened (hydrogenated)tallow fatty acid, obtained by splitting of tallow, washing out theglycerol, esterification of the tallow fatty acid with methanol, thenhardening (hydrogenation of the existing C--C double bonds) anddistillation. This methyl ester of a hardened tallow fatty acid had thefollowing values: iodine number 0.3; hydroxyl number 2.0; acid number0.6; saponification number 194.4, and was sulfonated as described above,neutralized, and bleached. After a bleaching time of 30 minutes, theKlett number of the ester sulfonated paste was 255.

EXAMPLE 1

The hardened methyl ester of tallow fatty acid used in ComparisonExample A was distilled before sulfonation by mixing with 0.5% byweight, based on the methyl ester of the fatty acid, of lithium aluminumhydride, and by heating to a sump temperature of 230°C./0.1 mbar. Thedistillation residue minus the lithium aluminum hydride was 8.5% byweight. The methyl ester of the hardened tallow fatty acid thus purifiedhad the following values: iodine number 0.; hydroxyl number 0; acidnumber 0.2; saponification number 194.3; and was sulfonated under theabove stated conditions, neutralized and bleached. After a bleachingtime of 30 minutes, the Klett number of the ester sulfonate paste was42.

EXAMPLE 2

The hardened methyl ester of tallow fatty acid used in ComparisonExample A was distilled before the sulfonation in the presence of 0.5%by weight, based on the methyl ester of the fatty acid, of aluminumchloride, and by heating to a sump temperature of 230°C./0.1 mbar. Thedistillation residue minus the aluminum chloride was 2.8% by weight. Thepurified hardened methyl ester of tallow fatty acid had the followingvalues: iodine number 0.2; hydroxyl number 0; acid number 0.2;saponification number 193.8; and was sulfonated as described above,neutralized, and bleached. After a bleaching time of 30 minutes, theKlett number of the ester sulfonate paste was 50.

EXAMPLE 3

The hardened methyl ester of tallow fatty acid used in ComparisonExample A was distilled before the sulfonation with an addition of 0.5%by weight, based on the methyl ester of the fatty acid, ofsodium-aluminum hydridotrimethylate NaAlH(OCH₃)₃ ; and by heating to asump temperature of 230°C./0.1 mbar. The distillation residue minus thecatalyst was 2.4% by weight. The purified hardened methyl ester oftallow fatty acid had the following values: iodine number 0.2; hydroxylnumber 0; acid number 0.3; saponification number 194.2; and wassulfonated as described above, neutralized, and bleached. After ableaching time of 30 minutes, the Klett number of the ester sulfonatepaste was 45.

COMPARISON EXAMPLE B

The starting material was a methyl ester of a hardened (hydrogenated)tallow fatty acid which had been obtained by splitting of tallow,washing out the glycerol, esterification of the tallow fatty acid withmethanol, hydrogenation of the existing C--C double bonds, anddistillation. This methyl ester of hardened tallow fatty acid had thefollowing values: iodine number 0.2; hydroxyl number 1.8; acid number0.2; saponification number 194.4; and was sulfonated as described above,neutralized, and bleached. After a bleaching time of 2 hours, the Klettnumber was 200.

EXAMPLE 4

The methyl ester of the hardened tallow fatty acid used as startingmaterial in Comparison Example B was distilled before the sulfonation inthe presence of 5% by weight, based on the methyl ester of fatty acid,of boric acid by heating to a sump temperature of 230° C./0.1 mbar. Thedistillation residue minus the boric acid present was 0.8% by weight.This methyl ester of tallow fatty acid was sulfonated in the statedmanner, neutralized, and bleached. After a bleaching time of 2 hours,the Klett number was 33.

COMPARISON EXAMPLE C

A methyl ester of a hardened tallow fatty acid, obtained as inComparison Example A, with the values: iodine number 0.3; hydroxylnumber 2.0; acid number 0.6; saponification number 194.4, was sulfonatedas described before, neutralized, and bleached. After a bleaching timeof 4 hours, the Klett number of the ester sulfonate paste was 200.

EXAMPLE 5

The methyl ester of the hardened tallow fatty acid used in ComparisonExample C was distilled before the sulfonation in the presence of 2% byweight, based on the methyl ester of the fatty acid, of aluminumstearate by heating to a sump temperature of 230° C./0.1 mbar. Thedistillation residue minus the aluminum stearate present was 3.5% byweight. The purified methyl ester of hardened tallow fatty acid havingan iodine number 0.3; hydroxyl number 0; acid number 0.8; saponificationnumber 194.1, was sulfonated as stated above, neutralized, and bleached.After a bleaching time of 4 hours, the Klett number of the estersulfonate paste was 50.

EXAMPLE 6

The hardened methyl ester of tallow fatty acid used in ComparisonExample C was distilled before the sulfonation with the addition of 1%by weight, based on the methyl ester of the fatty acid, or iron (III)chloride by heating to a sump temperature of 230° C./0.1 mbar. Thedistillation residue, minus the iron (III) chloride present, was 4.5% byweight. The thus purified methyl ester of hardened tallow fatty acidwith an iodine number 0.6; hydroxyl number <1; acid number 0.2;saponification number 194.0 was sulfonated as described above,neutralized, and bleached. After a bleaching time of 4 hours, the Klettnumber of the ester sulfonate paste was 80.

COMPARISON EXAMPLE D

The starting material was a methyl ester of a hardened tallow fattyacid, obtained by transesterification of tallow with methanol withsubsequent distillation and hardening (hydrogenation of existing C--Cdouble bonds). The ester obtained had the values: iodine number 0.55;hydroxyl number <1; acid number 0.4; saponification number 194.0. Thisester was sulfonated, neutralized, and bleached. After a bleaching timeof 30 minutes, the Klett number of the ester sulfonate paste obtainedwas 260.

COMPARISON EXAMPLE E

The methyl ester of tallow fatty acid used in Comparison Example D withthe iodine number 0.55 was further hardened to an iodine number of 0.1.This ester was sulfonated as described, neutralized, and bleached. Aftera bleaching time of 30 minutes, the Klett number of the ester sulfonatepaste was 180.

EXAMPLE 7

The rehardened methyl ester of tallow fatty acid used in ComparisonExample E was distilled before the sulfonation with addition of 0.5% byweight, based on the methyl ester of the fatty acid, of sodium-boronhydride by heating to a sump temperature of 230°C./0.1 mbar. Thedistillation residue was 2.8% by weight. The thus purified methyl esterof tallow fatty acid was sulfonated as described above, neutralized, andbleached. After a bleaching time of 30 minutes, the Klett number of theester sulfonate paste obtained was 40.

EXAMPLE 8

To prepare the catalyst, 379 gm of tallow fatty acid and 7.5 gm of boricacid were stirred for 3 hours at 200° C. Then the mixture obtained wasdistilled by heating to a sump temperature of 280° C./0.1 mbar. Therewere obtained 82 gm of a residue having a melting point of about 60° C.

The starting material used in Comparison Example E was distilled beforethe sulfonation in the presence of 1.5% by weight, based on the methylester of tallow fatty acid charged, of the catalyst by heating to a sumptemperature of 230° C./0.1 mbar. The distillation residue was 3% byweight. The distilled hardened methyl ester of tallow fatty acid wassulfonated in the manner described, neutralized, and bleached. After ableaching time of 30 minutes, the Klett number of the ester sulfonatepaste obtained was 27.

COMPARISON EXAMPLE F

The starting material was a hardened methyl ester of tallow fatty acid,obtained by transesterification of tallow with methanol with subsequentdistillation and hardening. This material was subjected to a seconddistillation. The obtained hardened methyl ester of tallow fatty acidwas free from glycerides and had the following values: iodine number0.25; hydroxyl number 1.0; acid number 0.2; saponification number 196.4.This ester was sulfonated in the described manner, neutralized, andbleached. After a bleaching time of 2 hours, the Klett number of theester sulfonate paste obtained was 95.

EXAMPLE 9

For the preparation of the catalyst, 500 gm of tallow fatty acid and 2.5gm of boric acid were stirred for one hour at 200° C./133 mbar, and themixture was then distilled by heating to a sump temperature of 280°C./0.1 mbar. The residue was 120 gm.

The starting material used in Comparison Example F was distilled beforethe sulfonation with addition of 1.3% by weight, based on the methylester of fatty acid, of the previously prepared catalyst, by heating toa sump temperature of 230° C./0.1 mbar. The distillation residue was1.6% by weight. The purified methyl ester of tallow fatty acid wassulfonated as described above, neutralized, and bleached. After ableaching time of 2 hours, the Klett number of the ester sulfonate pasteobtained was 30.

COMPARISON EXAMPLE G

The starting material was a methyl ester of a tallow fatty acid,obtained by transesterification of tallow with methanol followed bydistillation and hardening. The hardened material was subjected to asecond distillation. The obtained methyl ester of tallow fatty acid wasfree from glycerides and had the values: iodine number 0.2; hydroxylnumber 0.8; acid number 0.6; saponification number 196.6. This hardenedmethyl ester of tallow fatty acid was sulfonated as described,neutralized, and bleached. After a bleaching time of 30 minutes, theKlett number of the obtained ester sulfate paste was 135.

EXAMPLE 10

For the preparation of the catalyst, 320 gm of a mixture of 45% byweight of glycerol monostearate, 41% by weight of glycerol distearate,and 14% by weight of glycerol tristearate were stirred together with 62gm of boric acid for 3 hours at 160°C./66.5 mbar. The boric aciddissolved. The reaction product had a melting point of about 50° C.

The starting material used in Comparison Example G was distilled beforethe sulfonation in the presence of 0.9% by weight, based on the fattyacid ester charged, of the previously prepared catalyst, by heating to asump temperature of 230° C./0.1 mbar. The distillation residue was 1.7%by weight. The distilled hardened methyl ester of tallow fatty acid wassulfonated in the manner described, neutralized, and bleached. After ableaching time of 30 minutes, the Klett number of the ester sulfonatepaste obtained was 46.

EXAMPLE 11

The starting material used in Comparison Example F was distilled beforethe sulfonation in the presence of 1.0% by weight, based on the methylester of fatty acid, of zinc stearate, by heating to a sump temperatureof 230°C./0.1 mbar. The distillation residue was 2.0% by weight. Thedistilled hardened methyl ester of tallow fatty acid was sulfonated asdescribed, neutralized, and bleached. After a bleaching time of 2 hours,the Klett number of the ester sulfonate paste obtained was 47.

EXAMPLE 12

The starting material used in Comparison Example G was distilled beforethe sulfonation with an addition of 0.5% by weight, based on the methylester of fatty acid, of sodium methylate, by heating to a sumptemperature of 230°C./0.1 mbar. The distillation residue was 6.3% byweight. The purified methyl ester of tallow fatty acid was sulfonated bydescribed, neutralized, and bleached. After a bleaching time of 30minutes, the Klett number of the ester sulfonate paste was 40.

EXAMPLE 13

For the preparation of the catalyst, 379 gm of hardened tallow fattyacid (iodine number 0.3) and 7.5 gm of boric acid were stirred for 3hours at 200° C., and the mixture was subsequently distilled by heatingto a sump temperature of 280° C./0.1 mbar. There were obtained 82 gm ofa residue having a melting point of about 60° C.

In the starting material used in Comparison Example E, 1.5% by weight,based on the methyl ester of fatty acid charged, of the catalyst weredissolved. This mixture was transferred continuously, drop by drop, intoa distillation flask heated to 230° C. at 0.1 mbar, the inflow havingbeen regulated so that it matched the quantity distilling. Thedistillation residue was 2% by weight. The methyl ester of tallow fattyacid thus distilled was sulfonated as described before, neutralized, andbleached. After a bleaching time of 30 minutes, the Klett number of theester sulfonate paste obtained was 50.

EXAMPLE 14

The starting material was an unhardened tallow fatty acid, obtained bysplitting of tallow and washing out the glycerol. This tallow fatty acidwas distilled in the presence of 1% by weight, based on the fatty acidcharged, of sodium boron hydride, by heating to a sump temperature of230° C./0.1 mbar. The distilled tallow fatty acid and heated withmethanol in the weight ratio 1:1.1 in an autoclave for 2 hours at 200°C. Then unreacted methanol was removed by distillation. The residue wasagain admixed with 1.1 parts by weight of methanol to 1 part tallowfatty acid charged and again heated in the autoclave for 2 hours at 200°C. This operation was repeated once more after the distillation of theunreacted methanol from the reaction mixture. The methyl ester of tallowfatty acid then remaining after the distillation of the methanol washydrogenated with the addition of 0.3% by weight of Raney nickel, basedon the fatty acid ester charged, in an autoclave at 200°-220° C under ahydrogen pressure of 20 bar for a period of 2 hours. The hardened methylester of tallow fatty acid obtained after separation of the catalyst hadthe values: iodine number 0.1; hydroxyl number 0; acid number 5.9;saponification number 195.4. This ester was sulfonated in the describedmanner, neutralized, and bleached. After a bleaching time of 30 minutes,the Klett number of the ester sulfonate paste obtained was 42.

EXAMPLE 15

An unhardened tallow fatty acid, obtained by splitting of tallow andwashing out of glycerol, was hydrogenated under the conditions stated inExample 14. The hardened tallow fatty acid was then distilled in thepresence of 1% by weight, based on the charged acid, of sodium boronhydride, by heating to a sump temperature of 230° C./0.1 mbar. Thedistilled tallow fatty acid was then esterified with methanol under theconditions stated in Example 14. The obtained hardened methyl ester oftallow fatty acid with the values: iodine number 0.5; hydroxyl number 0;acid number 5.5; saponification number 198 was sulfonated as describedabove, and bleached. After a bleaching time of 2 hours, the Klett numberof the obtained ester sulfonate paste was 44.

EXAMPLE 16

An unhardened tallow fatty acid, obtained by splitting of tallow andwashing out the glycerol, was distilled with addition of 1% by weight,based on the fatty acid charged, of the catalyst from Example 10, byheating to a sump temperature of 230° C./0.1 mbar. The purified tallowfatty acid was esterified with methanol under the conditions stated inExample 14. The methyl ester obtained was hydrogenated under theconditions stated in Example 14. The hardened methyl ester of tallowfatty acid had the values: iodine number 0; hydroxyl number 0; acidnumber 5.4; saponification number 195.4, and was sulfonated in thestated manner, neutralized, and bleached. After a bleaching time of 30minutes, the Klett number of the obtained ester sulfonate paste was 50.

EXAMPLE 17

An unhardened tallow fatty acid, obtained by splitting of tallow andwashing out the glycerol, was hydrogenated under the conditions statedin Example 14. The hardened tallow fatty acid obtained was distilledwith addition of 5% by weight, based on the fatty acid charged, of thecatalyst from Example 10, by heating to a sump temperature of 230°C./0.1mbar. The distilled acid was then esterified with methanol under theconditions stated in Example 14. The hardened methyl ester of tallowfatty acid obtained had the values: iodine number 0.4; hydroxyl number0; acid number 2.7; saponification number 198, and was sulfonated asdescribed above, neutralized, and bleached. After a bleaching time of 2hours, the Klett number of the ester sulfonate paste obtained was 38.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, however, that other expedientsknown to those skilled in the art or disclosed herein may be employedwithout departing from the spirit of the invention or the scope of theappended claims.

We claim:
 1. A process for the preparation of sulfonated lower alkylesters of higher fatty acids comprising the steps ofA. subjecting freehigher fatty acids of plant and/or animal origin to purification by aheat treatment of from 150° to 280° C. in the presence of an amount ofan additive effective to reduce the hydroxyl number of said fatty acids,said additive being selected from the group consisting of esterificationcatalysts and carboxylic acid anhydrides, for a time sufficient toeffect an improvement in a subsequent sulfonation process, B. separatingpurified higher fatty acids from the treated material, C. esterifyingthe purified higher fatty acids with a lower alkanol underesterification conditions, D. recovering said lower alkyl esters ofhigher fatty acids, E. sulfonating said recovered esters and recoveringan α-sulfonated lower alkyl ester of said higher fatty acid which whenbleached has a Klett number of 60 or below.
 2. The process of claim 1wherein the heating time isfrom 0.1 to 60 minutes and the purifiedhigher fatty acids are separated by vacuum distillation at asubatmospheric pressure of from 0.1 to 10 torr.
 3. The process of claim1 wherein the starting free higher fatty acid is an unhardened tallowfatty acid.
 4. The process of claim 1 wherein said heat treatmenttemperature and said heat treatment time are mutually adjusted so thatan esterification or reesterification of free hydroxyl groups present inthe starting materials takes place without any other substantial changein the structure of said lower alkyl esters of higher fatty acids. 5.The process of claim 2 wherein the esterification catalyst is present inan amount of from 0.01 to 10% by weight of fatty acid starting materialand is a basic, neutral, or weakly acid catalyst which is soluble in thestarting material.
 6. The process of claim 2 wherein the additive is ahigh boiling carboxylic acid anhydride.
 7. A process for the preparationof sulfonated lower alkyl esters of higher fatty acids comprising thesteps ofA. subjecting free fatty acids of plant or animal origin topurification by a heat treatment at 200° to 250° C. for 0.1 to 60minutes in the presence of an amount of an additive selected from thegroup of esterification catalysts and carboxylic acid anhydrides, B.vacuum distilling the purified free fatty acids at a sub-atmosphericpressure of from 0.1 to 10 torr, C. esterifying the distilled, purifiedfatty acids with a lower alkanol under esterification conditions, D.recovering the lower alkyl esters of higher fatty acids, E. sulfonatingsaid recovered esters and F. recovering an α-sulfonated lower alkylester of said higher fatty acid which when bleached has a Klett numberof 60 or below.
 8. The process of claim 7 wherein the starting freehigher fatty acid is a tallow fatty acid and the lower alkanol containsfrom one to five carbon atoms.
 9. The process of claim 8 wherein thefatty acid is an unhardened tallow fatty acid and the alkanol ismethanol.
 10. The process of claim 7 wherein the esterification catalystused during step A is essentially neutral to alkaline reacting and issoluble in the starting material.
 11. The process of claim 10 whereinthe additive used in Step 1 is a high boiling carboxylic acid anhydride.12. The process of claim 7 wherein steps A and B are combined.
 13. Theprocess of claim 8 whrein the starting free higher fatty acid is ahardened methyl ester of a tallow fatty acid.